The disclosure relates to a hydrostatic traction drive and to a method for controlling the hydrostatic traction drive.
It is known that hydrostatic traction drives for mobile machines, such as for example wheel loaders or telescopic handlers, are equipped with hydraulic pumps and hydraulic motors which interact as a hydrostatic transmission in a hydraulic circuit, such as is presented for example in document DE 10 2010 045 541 A1 of the applicant. It is customary here that an internal combustion engine, for example a diesel engine, drives the hydraulic pump via a shaft. The hydraulic power of the pump is subsequently fed in the form of a volume flow and pressure to the hydraulic motor via the high-pressure side of the hydraulic circuit of the hydrostatic transmission, said motor in turn converting said hydraulic power into mechanical power. This mechanical power is composed of the rotational speed and the torque on the drive shaft of the hydraulic motor.
A basic design of such a hydrostatic traction drive is presented in document DE 42 06 833 C1.
The torque which is generated in this way is distributed to the front axle and rear axle in all-wheel-drive vehicles via distributed differentials. The axle differential, which distributes the torque made available for the respective axle further onto the individual wheels is located between the driven wheels of the respective axle. Differentials also serve here to equalize differences in rotational speed between the wheels or shafts, for example during the cornering of a dump truck, during which the wheels travel along paths of different lengths. In contrast, when the traction of a drive wheel is lost, undesired differences in rotational speed of the wheels occur. Loss of traction occurs when there is a sudden rise in the rotational speed of the respective drive wheel and a simultaneous reduction in the torque. The reduction of the torque relates here to the entire drive train. A possible path for recovering the lost traction of the drive wheel is to lock affected differentials. For this purpose differential locks are used which can be activated manually or in an automated fashion by means of locking clutches. In the locked state of the differential, the respective wheels or their shafts are connected to one another in a rotationally fixed fashion in order to equalize their rotational speed.
In order to avoid the loss of traction, a differential lock can be engaged automatically on the basis of characteristic speed signals, rotational speed signals or torque signals at which experience has shown that there is a risk of loss of traction.
Document EP 1 771 313 B1 discloses such a procedure. Here, the velocity and the torque are detected continuously by means of sensors and compared by a control unit in such a way that when predetermined threshold values of the velocity and of the torque are exceeded the differential locks are switched on, activated or engaged automatically in order to avoid loss of traction. When the threshold values are undershot, the differential lock is opened again.
However, it is disadvantageous with this solution that an actual loss of traction cannot be detected. Critical driving situations are merely defined by means of the experience-based threshold values in which the connection of the differential lock takes place, in order to prevent a potentially occurring loss of traction.
Contrary to the above, the disclosure is based on the object of providing a hydrostatic traction drive which is better protected against the loss of traction while having a simple design. Furthermore, the object is based on providing a method for controlling the traction drive with which loss of traction which occurs can be detected and a countermeasure can be initiated.